Very slow charge of a Li-Ion battery can be a problem?

[esm.]

Hi.

I have some PCBs that have a Lithium battery each, charged by a dedicated IC with a programmable current from 100 to 200mA, through a resistor RPROG.
The batteries are 3.7V of 3000 to 5000mAh. 4.2V floating voltage

Somebody know if is NOT recommended to make a very slow charge to these kind of batteries? Could that reduce their useful life-time?
The dedicated charger IC restarts the charge when the voltage of the Li-ion voltage goes 5% below the floating voltage (VFLOAT = 4,2V)

 

[Sceadwian]

Lithium batteries will not tolerate a float charge, it will destroy the chemistry. You MUST terminate the charge when the cell voltage reaches 4.1-4.2 volts or so. You must wait till the cells discharge bellow about 80% capacity before you attempt to charge them again.

 

[RCinFLA]

Slow charge is find. Just pay attention to the 4.2 v max / 2%C current charge termination.

 

[esm.]

Hi.
I didnt understand what you said: "Slow charge is find"

Just pay attention to the 4.2 v max / 2%C current charge termination.
The charger IC does this automatically with a maximum error of 1%, regarding the 4,2V float voltage.

EDIT:

After the BAT is fully charged (reached 4.2V), the charger IC automatically starts a new recharge cycle when the voltage of the BAT goes 95% below the float voltage (around 4.2V - 150mV is the recharge threshold voltage)
And the charger IC is produced by Linear technology, is not a chinese charger....

Please check attached picture

 

[RCinFLA]

Sorry, Slow charge in fine.

The charger IC looks like it triggers termination based on current tapering to 10% of its current limit setting. If you set it for 150 mA current limiting then it will not terminate charge until current drops to 15 mA. This might be too low for a large AH battery and it may never terminate the 4.2v voltage limiting stage of charging because a large AH battery may never drop to that level of current.

Check to see if charger IC and a time limit safeguard.

 

[esm.]

Sorry, Slow charge in fine.

The charger IC looks like it triggers termination based on current tapering to 10% of its current limit setting. If you set it for 150 mA current limiting then it will not terminate charge until current drops to 15 mA. This might be too low for a large AH battery and it may never terminate the 4.2v voltage limiting stage of charging because a large AH battery may never drop to that level of current.

Check to see if charger IC and a time limit safeguard.

I will test this in practice when possible.
And post the results here.

Automatic Recharge - LT4054L-4.2 DATASHEET
Once the charge cycle is terminated, the LTC4054L continuously monitors the voltage on the BAT pin using a comparator with a 2ms filter time (tRECHARGE). A charge cycle restarts when the battery voltage falls below 4.05V (which corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at or near a fully charged condition and eliminates the need for periodic charge cycle initiations

Looking at the typical application. When the BAT (90mAh) reaches 4.2V, its takes around 45 minutes until current falls to 10% of 90mA, so the charge is stoped. i don't know if this time is controlled by the IC or thats due to the battery capacity, only 90mAh

 

[WTP Pepper]

Using that IC will be fine. I use it at work, however the size of the pack will matter. Read the data sheet regarding end of charge conditions.

Hi.
I didnt understand what you said: "Slow charge is find"

Just pay attention to the 4.2 v max / 2%C current charge termination.
The charger IC does this automatically with a maximum error of 1%, regarding the 4,2V float voltage.

EDIT:

After the BAT is fully charged (reached 4.2V), the charger IC automatically starts a new recharge cycle when the voltage of the BAT goes 95% below the float voltage (around 4.2V - 150mV is the recharge threshold voltage)
And the charger IC is produced by Linear technology, is not a chinese charger....

Please check attached picture

 

[MrAl]

Hi,

Too slow of a charge rate is supposed to be bad for the cell. I've never actually measured anything to back this claim up though but that's hard to do. For one thing, we need to define what exactly a "slow charge" really is. Is it 10ma, 20ma, 50ma, 100ma ?
The cutoff current is supposed to be 1/20 times the cell rating in Ahr, but some guidelines suggest 1/33. So a 2Ahr cell should be cut out at either 100ma or 60ma.
What this means is that the lowest charge current should be either 60ma or 100ma for that cell. What happens if we charge at a lower current? Supposedly it hurts the cell beyond repair, so it is best to observe this guideline.

I charge my 1.8Ahr cells down to 50ma and have been using them for years. However, i also noticed that once the cells get down to 50ma it takes what seems like forever to get down lower than that. So i check the charger every hour and see what it is at, and if it is 50ma or less i turn it off. This seems to work quite well.

When it comes to charging any kind of battery, there is also a number that is usually referred to as the "Charge Acceptance" for that cell. This is a number that suggests that there is a certain minimum current level that is REQUIRED in order for the cell to actually get charged at all, even a little bit. Below this level, the cell gets little or no actual charge accumulation. I would think we might be able to combine this number with the cutoff current level and claim that the lowest charge level suggested by the cutoff current level is the lowest number that the cell can take before it stops even taking any further charge. With this in mind, we might want to always be sure to charge above the cutoff current and no lower than that, otherwise we might actually be not even charging the cell at all!

 

[audioguru]

A Lithium battery holds its charge for many years.
What is discharging your battery?

 

[esm.]

Hi. Just some uAmps (10 to 20uA) drawn by the charger IC when it enters in shutdown mode, after full charge of the BAT

 

[Sceadwian]

Slow charge is find. Just pay attention to the 4.2 v max / 2%C current charge termination.

You can slow charge a Lithium cell, but you cant not trickle or float charge one. What the poster meant by 'slow charge' is the constant current charge that is applied as a float charge to lead acid, NiCad, and even NimH cells. Lithium cell will NOT tollerate this float charge.

 

[Sceadwian]

AG, a primary lithium cell will hold it's charge for years. Lithium secondary cells will discharge to bellow optimal levels within 6 months to a year.

 

[esm.]

You can slow charge a Lithium cell, but you cant not trickle or float charge one. What the poster meant by 'slow charge' is the constant current charge that is applied as a float charge to lead acid, NiCad, and even NimH cells. Lithium cell will NOT tollerate this float charge.

Hi friend.
This is the question.
But about what you said, maybe I didn't understood well what you mean about trickle charging the BAT:

"but you cant not trickle"

All the charger ICs produced by Linear technology that I have seen (at least 4 different models) do a trickle charge, of around 10% (10 to 15mA) of the maximum programmed current, that is 100mA to 150mA in my case, being the capacity of the batteries from 3000mAh to 5000mAh.

All these ICs from Linear do a trickle charge when the voltage of the BAT is below 2,8~2,9V. After the BAT reached this voltage, it charges the BAT with the maximum programmed charge current (100~150mA) until it reaches the floating voltage of 4.2. Then the charging current begins to drop, and after drop to 10% of the maximum progammed current, it stops the charge, and only "restart" a new charge when the voltage of the BAT goes below 4,2V - (100 to 200mV), parameter called delta-recharge

 

[Sceadwian]

Food for thought... A Nicad has a generic charge efficiency range of 70-90-%, the cell resistance bleed off will suck up a modest trickle charge, and the chemistry isn't seriously temperature dependent. NimH's are only 66% charge efficient, the heat build up will kill them because of this, they are thermally sensitive.

Off the shelf secondary lithium's are 97-99% charge efficient... Once charged all additional current goes to keeping the cell in a voltage state that causes chemical degradation.

What you don't hear typically is that the reason for the failure of a secondary lithium cell is it being kept above an 80% charge state for too long a period of time, this is where 20% of a Lithium secondary batteries charge state comes from, yet it is the source of it's primary failure, chemical passivization.

Properly cycled lithium secondary cells will exist in a constant flux between 20% and 80% charge states, and NEVER ANY FURTHER, this is where the chemistry is stable!

 

[Sceadwian]

esm. Please plot the lifespan of cells treated in that manner with cell treated with a 20-80% charge state as a guide.

You treat Lithium chemistry like that you'll be lucky to get 8 months out of it..

Please research it I have.

 

[esm.]

What I noticed in practice is that even charging at 10~15mA, the voltage of the BAT quickly goes up to 2,8~2,9. Around 3-5 minutes, also with a 4000mAh BAT

EDIT: This is considering it has around 2,2~2,3V at the start of the charge. 2,2~2,3V is the UVLO voltage of the internal protection circuit inside the BATs, made by an internal dedicated IC

 

[Sceadwian]

Plot the current graph..

You do realize that these are active devices right?

 

[esm.]

Plot the current graph..

You do realize that these are active devices right?

Hi. What you mean with that?

If possible, plz take a look here also, from other forums:

https://www.edaboard.com/thread260347.html
https://forum.allaboutcircuits.com/showthread.php?t=72533
https://www.electronicspoint.com/very-slow-charge-li-ion-battery-can-problem-t250376.html

 

[Sceadwian]

I missed the 5% cutoff part. It is safe to charge a Lithium battery like this because it's not technically a float charge. Though for pack longevity it would be best to set the cutoff voltage to 4.1 volts. You don't get quiet as many mah's out of them but you increase the number of charge cycles.

It's not a float charge because a float charge is applied even after the battery is full, the chip you're using cuts the voltage off where it's supposed to.

 

[esm.]

This charge method used by Linear technology ICs could decrease lifetime of the battery?